Internet Protocol Multimedia Subsystem (IMS), which is an IP-based network architecture proposed in the 3rd Generation Partnership Project (3GPP), constructs an open and flexible service environment, supports multimedia applications and provides abundant multimedia services for users.
IMS, which is an IP-based telecom network architecture and is independent of access technology, can provide services for mobile cellular networks such as Global System for Mobile communications (GSM) and Universal Mobile Telecommunications System (UMTS), and so on, in addition to providing services for the Packet Switching access networks such as the General Packet Radio Service (GPRS), Wireless Local Area Network (WLAN), and so on.
The mobile cellular network, such as GSM and UMTS, applies the circuit switching technology, which is called a Circuit Switching (CS) domain and able to provide basic voice services and supplementary services based on voice services for users. When accessing to the IMS, the IMS evolves into an access mode, where services are provided entirely by the IMS. Such technology is called IMS Centralized Service (ICS for short).
The IMS centralized services have the following advantages:
(1) the IMS provides uniform services for access modes, such as circuit switching domain and packet switching domain, and supports network convergence;
(2) it supports the evolvement of a CS network into an IMS network; and
(3) it supports both a UE with ICS capability and an existing UE without ICS capability.
FIG. 1 is an illustration of an application scenario of session paths of the IMS centralized service, and it comprises the following network elements:
101: a User Equipment (UE);
102: a Visited Mobile Switch Center (VMSC);
103: a Home Subscriber Server (HSS);
104: a Media Gateway Control Function (MGCF);
105: a Media Gateway (MGW);
106: an IMS CS Control Function (ICCF);
107: a Call Session Control Function (CSCF);
108: a Telecom Application Server (TAS); and
109: a GSM Service Control Function (gsmSCF).
There are three paths between the UE 101 and the ICCF 106 to be established: a session control path, a bearer control path and a bearer path.
Wherein, the session control path comprises the following two modes:
(1) The CS session control path: which is in a CS domain and uses Unstructured Supplementary Service Data (USSD), and this path is via the VMSC 102 and the HSS 103;
(2) The PS session control path: which is in a PS domain and uses a Session Initiation Protocol (SIP) signaling, and the path is via the CSCF 107.
In the bearer control path, the UE 101 accesses to the VMSC 102 using standard CS control signaling and accesses to the IMS through the MGCF 104, and reaches the ICCF 106 through the CSCF 107.
In the bearer path, the UE 101 accesses to the IMS through the VMSC 102 and the MGW 105 and establishes a media connection with a remote UE of the session.
The IMS centralized services utilize the session control path between the UE 101 and the ICCF 106 to exchanges the session control message, and establish and control media bearer through the bearer control path, where the ICCF 106 acts as a User Agent (UA) of the IMS to access to the IMS on behalf of the UE.
The TAS 108 is the telecom application server in the IMS, and the basic telecom services are implemented in the TAS 108.
The function of the gsmSCF 109 is: when the VMSC triggers the mobile intelligent services (CAMEL, Customized Applications for Mobile network Enhanced Logic) to the gsmSCF 109, the gsmSCF 109 distributes the services request to the ICCF 106 according to the service information.
To date, there are mainly the following types of call forwarding in CS:
1) Call forwarding on unreachable
It is divided into the forwarding on phone powered off and the forwarding on no paging response and all incoming calls which call the UE are forwarded to a preset number.
2) Call forwarding on busy
The Call forwarding on busy is divided into forwarding on network-determined user busy and forwarding on user-determined user busy. Wherein, in the forwarding on network-determined user busy, when a UE is in a call, the other incoming calls are automatically forwarded to the preset number; in the forwarding on user-determined user busy, when a called user rings, the called user sends the user-busy message to the VMSC 102 depending on personal willingness thereof, and the VMSC 102 triggers the forwarding according to the message.
3) Call forwarding on no answer
When the phone is powered on and the incoming call is connected but is not answered, then the incoming call is automatically forwarded to another number preset.
4) Call forwarding unconditional
All phone numbers that call the UE are forwarded to another number preset.
In the CS domain, the forwarding service can be classified into the early forwarding and late forwarding, wherein, the early forwarding is that when acquiring the called user's roaming number, the home location register sends the forwarding message to the gateway mobile switch center to let the gateway mobile switch center trigger the forwarding service, such as the call forwarding on no conditions, call forwarding on phone powered off; while the late forwarding is that the call connects to the VMSC 102, but the call forwarding service is still triggered due to the call release by the user, such as the above call forwarding on busy, the call forwarding on no paging response, and the call forwarding on no reply etc.
In the present IMS centralized service, there is no complete solution for the forwarding on user-determined user busy, the forwarding on no paging response and the call forwarding on no reply etc.
Content of the Invention
The present invention provides a late call forwarding method in the IMS centralized service to overcome the shortcoming of the prior art and implement the late call forwarding on the basis of the network structure of the present IMS centralized service.
In order to solve the above problem, the present invention provides a late call forwarding method in an IP multimedia subsystem centralized service (ICS), and the method comprises the following steps of:
A1, during a call, an internet protocol multimedia subsystem circuit switch control function (ICCF) receiving a call request from a call session control function (CSCF) serving a called user, and the call being referred to as session A; the ICCF acquiring a called user's roaming number and initiates a call, being referred to as session B, to the called user;
A2, after receiving a call request of the session B, a visited mobile switch center (VMSC) serving the called user determining that a status of the called user satisfies conditions for triggering late call forwarding and the called user subscribes a late call forwarding service has the Originating-CAMEL Subscription Information (O-CSI) for the called user, then the VMSC triggering the late call forwarding service and triggers an intelligent service when initiating a call to a forwarding target; and
A3: said VMSC exchanging messages with said ICCF to inform said ICCF about session associated information and a forwarding reason, and when said ICCF determines that the forwarding is needed, said ICCF sending a response including corresponding indication to the session A or does not sending a response depending on the forwarding reason, and said CSCF relaying the indication to a telecom application server (TAS), and the TAS initiating a regular forwarding service.
Furthermore, in the step A2, said conditions for triggering said late call forwarding comprises call forwarding on user-determined user busy, call forwarding on no paging response or call forwarding on no answer.
Furthermore, in the step A3, said VMSC exchanging the intelligent service message with said ICCF comprises the following steps of:
A311. said VMSC sending the intelligent service message including the session associated information and the forwarding reason to the global system for mobile communications service control function (gsmSCF), and said gsmSCF forwarding the message to said ICCF; and
A312. after said ICCF determining that the message relates with the sessions A and B according to the session associated information in the received intelligent service message, said ICCF determining that the forwarding is needed and then sending a customized applications for mobile network enhanced logic (CAMEL) failure message to said VMSC, and the failure message reaching said VMSC via said gsmSCF.
Furthermore, in the step A3, said VMSC exchanging the intelligent service message with said ICCF comprises the following steps of:
A321. said VMSC sending the intelligent service message including the session associated information and the forwarding reason to the gsmSCF, and said gsmSCF forwarding the message to said ICCF;
A322. after said ICCF determining that the message associates with the sessions A and B according to the session associated information in the received intelligent service message, said ICCF allocating a temporary IMS routing number (IMRN) and associating the IMRN with said sessions A and B, storing the forwarding reason, and then returning the IMRN to said VMSC through CAMEL connection message, and said CAMEL connection message reaching said VMSC via said gsmSCF;
A323. after receiving the CAMEL connection message, said VMSC taking said IMRN as a called number to initiate a session C;
A324. after receiving a call request for the session C, said ICCF determining that the session C associates with the sessions A and B according to said IMRN and that the forwarding is needed, then sending the response message to CSCF in the session A including corresponding indication.
Furthermore, in the step A311 or A321, said intelligent service message including the session associated information and the forwarding reason is an Initial Detection Point (IDP) message.
Furthermore, said forwarding reason is indicated in a field of the called number or a forwarding reason in said IDP message.
Furthermore, said session associated information is a calling number or an original called number in the IDP message; alternatively, said session associated information is the calling number and the original called number in the IDP message.
Furthermore, step A3 applies the following way to release the session B:
After determining that the received intelligent service message associates with the sessions A and B, said ICCF releasing the session B;
Alternatively, after receiving a customized applications for mobile network enhanced logic (CAMEL) failure message from said ICCF, said VMSC releasing the session B;
Alternatively, after said ICCF determines that the received intelligent service message associates with the sessions A and B, said ICCF releasing the session B; meanwhile, after said VMSC receives the CAMEL failure message from said ICCF, said VMSC also releasing the session B.
Furthermore, the step A3 applies the following way to release the sessions B and C:
After determining that the session C associates with the sessions A and B, said ICCF releasing the sessions B and C;
Alternatively, after said ICCF determines that the session C associates with the sessions A and B, said ICCF releasing one of the sessions B and C, and after said VMSC receives the release message, said VMSC releasing the other session;
Alternatively, after said ICCF determines that the session C associates with the sessions A and B, said ICCF releasing the sessions C and B; and after said VMSC receives a first arriving releasing message of either of the sessions C and B, said VMSC releasing the other session. Furthermore, in the step A3, when the forwarding reason is call forwarding on no answer, said ICCF returns a corresponding session initiation protocol (SIP) failure response message in the session A, and after said TAS receives the message, said TAS initiates a call forwarding on no answer service according to said SIP failure response message; alternatively, said ICCF does not send any response message to the TAS, and the TAS waits for an expiration and triggers the call forwarding on no answer;
Alternatively, if the forwarding reason is a call forwarding on user-determined user busy or call forwarding on no paging response, said ICCF returns a corresponding SIP failure response message to the session A, and after said TAS receives the message, said TAS initiates the call forwarding on user-determined user busy or the call forwarding on no paging response according to the SIP failure response message.
Furthermore, in the step A2, when the called user registers in a circuit switching domain, subscription data of the called user which includes late call forwarding service and the O-CSI are downloaded to said VMSC, and said VMSC triggers said late call forwarding service and the intelligent service according to the subscription data and the status of the called user.
The technical effects of the present invention are as follows:
1. The present invention provides a method for implementing the late call forwarding in the IMS centralized service to implement the late call forwarding with a relatively simple message interaction process based on the present network architecture and the communication standard.
2. The present invention sends the forwarding reason to the IMS domain through the method of the calling intelligent service to control the late call forwarding service in the IMS domain, thus achieve the IMS centralized service control of the late call forwarding.